Spark plug electrode



Patented May 21, 1935 UNITED STATES PATENT OFFICE SPARK PLUG ELECTRODE Donald w. Randolph, Flint, Mich., assignor, by

mesne assignments, to General Motors Corporation, Detroit, Micln, a corporation of Delaware No Drawing. Application May ii, 1932, Serial N0. 609,771

11 Claims.

,5 the presence in the alloy of an element for reducing the sparking voltage. The elements suitable for this purpose are characterized by low work function; that is, but a small amount of energy is necessary to remove an electron from the element. The elements are also characterized in general by the fact that they are strongly electropositive, and, viewed from a theoretical standpoint only, comprise the alkali and alkaline earth metals. However, as set forth in the said patent, the elements that are of any practical value, at least from the standpoint of spark plug use, are the alkaline earth metals, calcium, stron tium and barium.

Not only is it desirable that spark plug electrodes contain elements capable of reducing the sparking voltage, but it is likewise essential that they be of such material as to have good heat conductivity and good resistance to heat and corrosion. Nickel and especially alloys of nickel and manganese have heretofore been found to be particularly desirable from the point of view of the last named qualities. Consequently in carrying the Dufiendack and Rabezzana invention into practice, an element or elements adapted to reduce the sparking voltage has been combined with nickel or with a nickel-manganese alloy. As set forth in the said specification, after experiments with the elements of the above group, barium was found to be the most desirable because it is not readily removed from the alloy. As a result the barium is available in the electrodes throughout' their life and functions at all times to maintain a low sparking voltage. In addition the barium greatly improves the resistance to corrosion.

While the 'nickel-manganese-barium alloy, described and claimed in the said specification represents a decided advance in spark plug electrodes, and the. alloy has been found, in practice,

to possess to a high degree the properties of good heat conductivity, high resistatnce to heat and corrosion and low sparking voltage, I have succeeded in greatly improving the resistance to corrosion by adding chromium, to the alloy. In previous tests with the nickel-manganese alloy it was found that the addition of chromium in amounts up to 5% added somewhat to the resistance to corrosion, although the addition of more than this amount decreased the heat conducting properties of the alloy to such an extent that corrosion took place at a faster rate than with the chromium omitted.

I have now found that theaddition of chromium to the barium-nickel-manganese alloy produces a further and very marked increase in resistance to corrosion. To get the best results the amount of chromium added to the alloy should not exceed 10%. The preferred composition of the alloy is as follows:

However, for spark plug use, I prefer the following composition:

Manganese Zero to 2% Chromium .5 to 10% Barium .01 to 20% Magnesium. A trace Balance nickel The barium content is not critical. Very substantial reduction in sparking voltage maybe obtained with amounts as low as .01 For spark plug use a barium content of around .03% together with a chromium content around 4% will be found to be very satisfactory with present day ignition equipment. I have found that the amount of emission with the chromium content less than .5% is insufficient for practical purposes for its efiect on electronic emission and resistance to corrosion, while perceptible, is not sufiicient for practical use. However, with respect to the lower limit of both barium and chromium, these amounts are purely practical limits for even smaller proportions will produce the same effect although in less degree.

For some purposes it may be desirable to substitute in whole or in part for the base metal, nickel, the kindred metal, cobalt, although this will result in an increased rate of corrosion and reduced emission. Other metals which may be employed as diluents will occur to those skilled in the art.

Manganese acts in the usual manner to prevent intercrystalline corrosion. Other known deoxidizers increasing the workability of the metal may be used in place of manganese.

The amount of magnesium present in the alloy is so small, so difficult to measure by ordinary methods of chemical analysis, and so non-uniformly distributed that it has been designated as a trace. It is the residue of about .1% .mag-

nesium added to deoxidize the alloy and increase its ductility so as to permit easy drawing.

In preparing the alloy it is important, if the best results are to be obtained, that the amount of iron occurring as an impurity be kept to a minimum.

The alloy may be prepared by wrapping the barium in nickel foil, inclosing it in a practically air tight container, or otherwise preparing it to exclude moisture and prevent oxidation, and immersing it in the melt. The melt is maintained at a temperature somewhat above that of fusion, and, after allowing just sufllcient time for the barium-to permeate the mass, it is poured into ingot form, and drawn to the desired shape. In accordance with usual practice in the making-of nickel alloys for drawing, there is preferably introduced into the base metal prior to the introduction of barium a small percentage of magnesium, about .1%.

In order to obtain the higher barium contents it is best to employ the method described and claimed in my copending application Serial No. 520,704, filed March 6, 1931.

A further study of the effect of chromium on the other constituents of the alloy herein disclosed indicates that it not only increases resistance to corrosion, but also materially increases electronic emission of the electrode, and prevents evaporation of the alloy.

The use of calcium and strontium in p1ace of barium is, 01 course, indicated since these ma- .terials are well known to have low work function, and are commonly used as coatings for oxide coated cathodes. However, their rate of emission is much inferior to that of barium.

This casev is a continuation, in part, of my prior application Serial No. 520,703, filed March 6, 1931, which in turn was a continuation, in part, of my prior application Serial No.'351,835, filed April 1, 1929.

1. A spark plug having an electrode made of an alloy having as its major constituent a base metal such as nickel-cobalt metal, a metal of the alkaline earth group to reduce thev sparking voltage, and chromium to increase emissivity, resist corrosion and retard evaporation of the metal.

'2.-An electrode for spark plugs and the like made of an alloy of nickel, an alkaline earth metal and chromium.

3. A spark plug having an electrode made of an alloy of nickel, chromium and barium.

4- A spark plug having an electrode made of an alloy consisting essentially of nickeland containing from .5 to 10% chromium and from .01 to .20% barium.

5. A spark plug having an electrode made of an alloy of nickel-cobalt metal, chromium, an alkaline earth metal and a deoxidizer.

6. A spark plug having an electrode made of an alloy of nickel, chromium, barium and manganese. i

7. A spark plug having an electrode made of an alloyconsisting essentiallyof nickel and containing from .5 to 10% chromium and from .01 to" .20% barium, and a small proportionof a deoxidizing material. v

8. A spark plug having an electrode made of analloy consisting essentially of nickel and contain- .ing from .5 to 10% chromium, from .01 to .20%

barium, and from zero to 2% manganese.

9. A spark plug electrode made of an alloy consisting of nickel, an alkaline earth metal, and chromium; the alkaline earth metal being present in an amount between .01 and .80%, the nickel being present in a preponderating proportion, and the balance being chromium.

10. A spark plug electrode made of an alloy consisting of nickel, barium and chromium; barium being present in an amount between .0l% and .80%, the nickel being present in a preponderating proportion, and the balance being chromium.

11. A spark plug having an electrode made of an alloy consisting of from .5% to 10% chromium, from .01% to .20% barium, up to 2% magnesium, and the balance nickel.

DONALD W. RANDOLPH. 45 

